<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>


    <style>
        body{
            background: linen;
        }

        div{
            width: 500px;
            height: 500px;
            background: linear-gradient(white 50%,black 50%);
            margin: 10px auto;
            display: flex;
            align-items: center;
            border-radius: 50%;
        }

        div::before{
            content:"";
            width: 250px;
            height: 250px;
            background: radial-gradient(white 25%,black 25%);
            border-radius: 50%;
        }

        div::after{
            content:"";
            width: 250px;
            height: 250px;
            background: blue;
            background: radial-gradient(black 25%,white 25%);
            border-radius: 50%;
        }

    </style>

</head>
<body>
    

    <div>


    </div>

</body>
</html>